We would like to thank the Fertilab Andrology clinic, especially Jos&#233; Mar&#237;a Montes and Andrea Torrents, for allowing us access to donors. Funding: A.C. is supported by grants from Universidad de la Rep&#250;blica (CSIC_2018, Espacio Interdisciplinario_2021). Additional funding was obtained from the Programa de Desarrollo de Ciencias B&#225;sicas (PEDECIBA, Uruguay). P.I. and R.S. are supported by Universidad de la Rep&#250;blica (I+D, CSIC 2014; I+D, CSIC 2016, Iniciaci&#243;n a la Investigaci&#243;n, CSIC 2019 and FMV_1_2017_1_136490 ANII- Uruguay). P.I. is supported by POS_FMV_2018_1_1007814 and CAP-UDELAR 2020. The figures were illustrated using Biorender.com.

The experiments were approved by the Ethics Committee of the Facultad de Medicina de la Universidad de la Rep&#250;blica, Montevideo, Uruguay.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/65493/65493fig01.jpg" /> 
Figure 1: Workflow for high-resolution respirometry to assess mitochondrial function in intact and permeabilized human sperm. The protocol was divided into four different steps: 1) preparation of the sample, 2) oxygen calibration in the Oroboros instrument, 3) oxygen consumption measurement for intact and permeabilized cells, and 4) data extraction from the equipment and analysis. Abbreviations: CASA = computer-assisted sperm analysis; BWW = Biggers Whitten Whittingham medium; MRM = mitochondrial respiration medium; ADP = adenosine diphosphate; FCCP = carbonyl cyanide -p- trifluoromethoxyphenylhydrazone; AA = antimycin A. <a href="https://www.jove.com/files/ftp_upload/65493/65493fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
NOTE: The workflow for measuring the oxygen consumption in sperm cells using HRR is shown in Figure 1. Information on the materials, equipment, and reagents used in the protocol is presented in the Table of Materials.
1. Sample preparation
<ol>
	<li>Sample collection
	<ol>
		<li>Collect freshly ejaculated human semen by masturbation after a recommended 3 day abstinence in a sterile plastic container. Transport the samples immediately to the laboratory.</li>
		<li>Incubate the samples for 30-60 min at room temperature (RT) to liquefy completely24.</li>
		<li>After liquefaction, store the samples at 37 &#176;C until the experiment begins.</li>
	</ol>
	</li>
	<li>Sperm evaluation with computer-aided sperm analysis (CASA)
	<ol>
		<li>Mix the sample, and load 7 &#181;L into a pre-warmed sperm counting chamber.</li>
		<li>Place the chamber on the pre-warmed (37&#160;&#176;C) stage of a direct light microscope.</li>
		<li>Open the computerized sperm analysis software and, enter the motility and concentration module (click on Mot).</li>
		<li>Select the configuration that corresponds to human sperm conditions. 
		NOTE: The configuration must be adapted to the type and depth of the chamber as well as to the sample species and the system CASA.</li>
		<li>Randomly analyze 10 different fields per chamber by clicking on the Analyze button.</li>
		<li>Click on Results to obtain the sample concentration and motility.</li>
	</ol>
	</li>
	<li>Cell preparation 
	NOTE: If the HRR is not calibrated, start with steps 2.1-2.2 before preparing the cells (step 1.3). It is important to measure the oxygen consumption immediately when the sperm cells are resuspended in the medium.
	<ol>
		<li>Centrifuge the samples at 400 x g for 10 min at RT.</li>
		<li>Remove the seminal plasma, and resuspend the spermatozoa in 2 mL of Biggers Whitten Whittingham (BWW) for experiments with intact cells or mitochondrial respiration medium (MRM) for studies with permeabilized cells. The compositions of the media are shown in Table 1.</li>
		<li>Repeat the steps described in step 1.2 for sperm concentration studies.</li>
	</ol>
	</li>
</ol>
2. High-resolution respirometry: OXPHOS analysis
NOTE: HRR integrates highly sensitive oxygraphs (Oxygraph-2 K; Oroboros Instruments GmbH, Innsbruck, Austria) with software (DatLab, version 4.2; Oroboros Instruments GmbH). The experimental data are displayed as the oxygen concentration versus time (as pmol of O2/106 cells&#183;min&#8722;1) and as real-time transformations of these data, allowing the experimenter to track the respiration (oxygen consumption, oxygen flux) of biological and biochemical samples while the experiment is still running. The HRR can be used to follow the respiration of living and motile cells, which is particularly useful for sperm, whose motility is associated with the sperm quality and fertility potential. The laboratory uses an HRR Oroboros Oxygraph2-k, Oroboros Instruments, with two chambers. The steps described in this protocol must be performed independently for both 2 mL chambers.
<ol>
	<li>Equipment preparation
	<ol>
		<li>Turn on the HRR, and connect it to the respirometry software (DatLab) for data acquisition and analysis.</li>
		<li>Replace the 70% ethanol in the oxygraph chamber with ddH2O. Stir it continuously with the magnetic stir bar in the chamber at 750 rpm. Let it stand for 10 min, and aspirate the double-distilled (dd) H2O afterward.</li>
		<li>Wash the chamber three times with ddH2O for 5 min each time. 
		NOTE: This step is necessary to remove the remaining ethanol from the chambers. Sperm cells are very sensitive to ethanol. The recording could be compromised if this step is omitted.</li>
	</ol>
	</li>
	<li>Calibration of the oxygen sensors 
	NOTE: The calibration procedure varies slightly depending on the instrument. Perform an air calibration of the polarographic oxygen sensor as described by the manufacturer25. In this section, the calibration protocol is explained briefly.
	<ol>
		<li>Remove the ddH2O, and pipette 2 mL of the same medium used for the cell preparation into the chamber. Place the stoppers, leaving an air exchange bubble. 
		NOTE: It is important to know the volume of the chamber to determine the exact volume of medium needed.</li>
		<li>Record the oxygen calibration values (click on Layout &#62; 01 Calibration Exp. Gr3-Temp) to monitor the performance of the sensor membrane by stirring the medium with the stir bar at 750 rpm for at least 30 min at 37 &#176;C. Use the other settings as mentioned: gain for sensor: 2; polarization voltage: 800 mV; data recording interval: 2.0 s. 
		&#8203;NOTE: It is expected to obtain an O2 slope uncorrected (red line) within &#177;2 pmol&#8729;s&#8722;1&#8729;mL&#8722;1 with a stable signal from the polarographic sensor.</li>
		<li>Drag the mouse while holding down the left mouse button and the shift key to select an area where the change in oxygen concentration (Y1 O2 Concentration, blue line) is stable.</li>
		<li>Open the O2 Calibration window (click on Oxygraph &#62; O2 Calibration). In Air Calibration, change the selected mark to the region selected in step 2.2.3. Finish by clicking on Calibrate and Copy to Clipboard.</li>
		<li>Stop the recording, and save by clicking on Oxygraph &#62; Ok Control &#62; Save and Disconnect. 
		NOTE: This dataset must be saved so that it can be used in all of the day&#39;s experiments. The calibration is only performed once per day for each medium.</li>
	</ol>
	</li>
	<li>Digitonin-permeabilization titration
	<ol>
		<li>Open the chamber, and aspirate the medium inside.</li>
		<li>Load in the chamber at least 24 x 106 and no more than 70 x 106 sperm cells in a final volume of 2 mL of MRM. 
		&#8203;NOTE: It is important to measure the number of cells in the chamber in order to adjust the oxygen consumption at the end of the experiment. A lower number of cells than recommended cannot be measured.</li>
		<li>Close the chamber by pushing the stoppers all the way in, and aspirate the remaining liquid at the top. Start the experiment with the same settings as for the calibration: stirring speed: 750 rpm; temperature: 37 &#176;C; gain for sensor: 2; polarization voltage: 800 mV; and data recording interval: 2.0 s.</li>
		<li>To load the calibration, double-click on the Pos Calib box in the bottom corner. Open the calibration performed in step 2.2 (click on Oxygraph &#62; O2 Calibration &#62; Copy from File), and click on Calibrate and Copy to Clipboard. 
		NOTE: The POS Calib box will change from yellow to green. The data are displayed in oxygen flow corrected per volume charts (Layout 05 Flux per Volume uncorrected). Different layouts are available in Oxygraph &#62; Layout.</li>
		<li>Add 5 &#181;L of 0.5 M adenosine diphosphate (ADP), 10 &#181;L of 2 M glutamate, and 2.5 &#181;L of 0.4 M malate (final concentrations: 1.25 mM, 10 mM, and 0.5 mM). Measure the oxygen consumption until the signal stabilizes. 
		NOTE: Precision Hamilton micro-syringes are used for injection through the loading port in the stopper. Use one syringe per drug to avoid cross-contamination. Click on F4 to register, and mark in the oxygen register when a treatment is added. 
		NOTE: The substrates are prepared in ultrapure water and stored at &#8722;20 &#176;C for 3 months.</li>
		<li>Tritate by adding 1 &#181;L of 10 mM digitonin in successive steps until the oxygen consumption reaches a maximal level. 
		NOTE: Thorough washing with water, 70% ethanol, and 100% ethanol is essential if the same chamber is used for two experiments on the same day. 
		NOTE: Digitonin is prepared in ultrapure water and stored at &#8722;20 &#176;C for 3 months.</li>
	</ol>
	</li>
	<li>Routine respiratory assessment protocol for intact and permeabilized sperm cells (complex I or complex II)
	<ol>
		<li>Open the chamber, and aspirate the medium inside.</li>
		<li>Load in the chamber at least 24 x 106 and no more than 70 x 106 sperm cells in a final volume of 2 mL of BWW (intact cell analysis) or MRM (permeabilized cell analysis).</li>
		<li>Start the experiment with the same settings as for the calibration (this is described in step 2.3.3).</li>
		<li>Load the calibration performed in step 2.2 as described in step 2.3.4.</li>
		<li>Record the respiration of the cells for at least 5 min until a stable signal is obtained. This measurement corresponds to basal respiration in intact cells.</li>
		<li>If the experiment is with intact cells, proceed to step 2.4.9. For permeabilized cells, inject 4.5 &#181;L of 10 mM digitonin (final concentration: 22.5 &#181;M). Permeabilize the cells for 5 min.</li>
		<li>Add the substrates: 10 &#181;L of 2 M glutamate and 2.5 &#181;L of 0.4 M malate (final concentrations: 10 mM and 0.5 mM, respectively) for complex I or 20 &#181;L of 1 M succinate (final concentration: 10 mM) for complex II. Measure the oxygen consumption until the signal increases and stabilizes. This is state 4, which means basal complex I or basal complex II supported respiration in the absence of ADP. 
		NOTE: The substrates are prepared in ultrapure&#160;water and stored at &#8722;20 &#176;C for 3 months.</li>
		<li>Inject 5 &#181;L of 0.5 M ADP (final concentration: 1.25 mM). Measure the oxygen consumption until the signal increases and stabilizes. The addition of ADP increases the signal corresponding to the maximum oxygen consumption through complex I or complex II (state 3, in permeabilized cells).</li>
		<li>Add 1 &#181;L of 4 mg/mL oligomycin (final concentration: 2 &#181;g/mL), an ATP synthetase inhibitor. Measure the oxygen consumption until the signal decreases and stabilizes. 
		NOTE: Oligomycin is prepared in ethanol and stored at &#8722;20 &#176;C for 3 months.</li>
		<li>Titrate by adding 1 &#181;L of 0.1 mM to 1 mM carbonyl cyanide-P- trifluoromethoxy-phenylhydrazone (FCCP) in successive steps until a maximum uncoupled respiration rate is reached. Measure the oxygen consumption until the signal increases and stabilizes. 
		NOTE: FCCP is prepared in ethanol and stored at &#8722;20 &#176;C for 3 months.</li>
		<li>The final concentration of FCCP is sample-dependent. Stop injecting the drug when oxygen consumption begins to decrease.</li>
		<li>Finally, inject 1 &#181;L of 5 mM antimycin A (2.5 &#181;M final concentration). This is a complex III inhibitor to discriminate between the mitochondrial and residual oxygen consumption (non-mitochondrial respiration). For the analysis of complex I, add 1 &#181;L of 1 mM rotenone (0.5 &#181;M final concentration), an inhibitor of this complex, instead of AA. Measure the oxygen consumption until the signal decreases and stabilizes. 
		&#8203;NOTE: The drugs are prepared in ethanol and stored at &#8722;20 &#176;C for 3 months.</li>
	</ol>
	</li>
</ol>
3. Data extraction and analysis
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/65493/65493fig2v2.jpg" /> 
Figure 2: Acquisition of respiratory parameters from a high-resolution respirometry experiment. (A,B) Schematic representations of graphs obtained, as described in Figure 1, for intact and permeabilized cells, respectively. These parameters have been previously described15. <a href="https://www.jove.com/files/ftp_upload/65493/65493fig2v2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<ol>
	<li>Drag the mouse by pressing the left mouse button and the shift key to select regions where the oxygen flux per volume correlated (Y2 O2 slope uncorr., red line) is stable after the injection of a substrate or inhibitor. Figure 2 shows the different parameters obtained from the register previously described15. 
	NOTE: The parameters depend on the experiment; all of them are as follows: basal respiration in intact cells and respiration in the presence of glutamate/malate or succinate (state 4), ADP (state 3), oligomycin (proton leak), FCCP (maximum respiration rate), rotenone/AA (non-mitochondrial respiration). In permeabilized cells, basal respiration corresponds to state 3.</li>
	<li>Click on the Marks &#62; Statistics windows, and export the data.</li>
	<li>Normalize the data obtained per 1 million sperm cells. The units of the slopes are pmolO2&#183;s&#8722;1&#183;mL&#8722;1&#183;10&#8722;6 cells.</li>
	<li>Subtract the non-mitochondrial oxygen consumption from all the values before calculating the indices.</li>
	<li>Calculate the indices using the various equations previously described15: 
	<img alt="Equation 1" src="/files/ftp_upload/65493/65493eq01v3.jpg" style="margin: auto;" /></li>
</ol>

Determining Respiration in Human Sperm Cells by High-Resolution Respirometry

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W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Concepts+in+sperm+heterogeneity,+sperm+selection+and+sperm+competition+as+biological+foundations+for+laboratory+tests+of+semen+quality.">Concepts in sperm heterogeneity, sperm selection and sperm competition as biological foundations for laboratory tests of semen quality.</a> Reproduction. 127 (5), 527-535 (2004).</li><li>Sousa, A. P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Not+all+sperm+are+equal:+Functional+mitochondria+characterize+a+subpopulation+of+human+sperm+with+better+fertilization+potential.">Not all sperm are equal: Functional mitochondria characterize a subpopulation of human sperm with better fertilization potential.</a> PloS One. 6 (3), e18112 (2011).</li><li>Moscatelli, N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Single-cell-based+evaluation+of+sperm+progressive+motility+via+fluorescent+assessment+of+mitochondria+membrane+potential.">Single-cell-based evaluation of sperm progressive motility via fluorescent assessment of mitochondria membrane potential.</a> Scientific Reports. 7, 17931 (2017).</li><li>Ferreira, J. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Increased+mitochondrial+activity+upon+CatSper+channel+activation+is+required+for+mouse+sperm+capacitation.">Increased mitochondrial activity upon CatSper channel activation is required for mouse sperm capacitation.</a> Redox Biology. 48, 102176 (2021).</li><li>Irigoyen, P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mitochondrial+metabolism+determines+the+functional+status+of+human+sperm+and+correlates+with+semen+parameters.">Mitochondrial metabolism determines the functional status of human sperm and correlates with semen parameters.</a> Frontiers in Cell and Developmental Biology. 10, 926684 (2022).</li></ol>

The authors have nothing to disclose.

HRR critically depends on several steps: (a) the equipment maintenance, (b) accurate calibration of the oxygen sensors, (c) the uncoupler titration26, and finally, (d) the adequate use of indices representing the mitochondrial function. The equipment maintenance is crucial. It is recommended to replace the membranes of the polarographic oxygen sensor regularly and to correct the instrumental background. Extensive washing after the collection of spermatozoa from the chambers is essential to obtain ...

An erratum was issued for:&#160;<a href="https://www.jove.com/t/65493">High-Resolution Respirometry to Assess Mitochondrial Function in Human Spermatozoa</a>. The Protocol and Representative Result&#160;sections were&#160;updated.
Step 2.4.12 of the Protocol was updated from:
Finally, inject 1 &#181;L of 5 mM antimycin A (2.5 &#181;M final concentration). This is a complex II inhibitor to discriminate between the mitochondrial and residual oxygen consumption (non-mitochondrial respiration). For the analysis of complex I, add 1 &#181;L of 1 mM rotenone (0.5 &#181;M final concentration), an inhibitor of this complex, instead of AA. Measure the oxygen consumption until the signal decreases and stabilizes.
to:
Finally, inject 1 &#181;L of 5 mM antimycin A (2.5 &#181;M final concentration). This is a complex III inhibitor to discriminate between the mitochondrial and residual oxygen consumption (non-mitochondrial respiration). For the analysis of complex I, add 1 &#181;L of 1 mM rotenone (0.5 &#181;M final concentration), an inhibitor of this complex, instead of AA. Measure the oxygen consumption until the signal decreases and stabilizes.
Figure 3 in the Representative Results section was updated from:
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/65493/65493fig03.jpg" /> 
Figure 3: Determination of the optimal concentration of digitonin for the permeabilization of human sperm cells. The respiration rates were measured at 37 &#176;C in MRM medium with glutamate, malate, and adenosine diphosphate. (A) Representative respiratory trace. The blue line is the O2 concentration, and the red line represents the O2 flow per volume correlated. (B) Mitochondria respiration rate means &#177; standard error, n = 4. The red arrow represents the optimal concentration. Abbreviation: dig = digitonin. <a href="https://www.jove.com/files/ftp_upload/65493/65493fig03large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
to:
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/65493/65493fig3v2.jpg" /> 
Figure 3: Determination of the optimal concentration of digitonin for the permeabilization of human sperm cells. The respiration rates were measured at 37 &#176;C in MRM medium with glutamate, malate, and adenosine diphosphate. (A) Representative respiratory trace. The blue line is the O2 concentration, and the red line represents the O2 flow per volume correlated. (B) Mitochondria respiration rate means &#177; standard error, n = 4. The red arrow represents the optimal concentration. Abbreviation: dig = digitonin. <a href="https://www.jove.com/files/ftp_upload/65493/65493fig3v2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

An erratum was issued for:&#160;<a href="https://www.jove.com/t/65493">High-Resolution Respirometry to Assess Mitochondrial Function in Human Spermatozoa</a>. The Protocol and Representative Result&#160;sections were&#160;updated.

Erratum: High-Resolution Respirometry to Assess Mitochondrial Function in Human Spermatozoa

Male infertility is estimated to account for 40%-50% of all cases of infertility in couples1. Conventional semen analysis plays a crucial part in determining male fertility; however, approximately 15% of infertile men have normal sperm parameters2. In addition, routine semen analysis provides limited information about sperm function and does not reflect subtle sperm defects3.
Sperm mitochondria have a special structure, as they are arranged as a helical sheath around the flagella. The mitochondrial sheath contains a variable number of mitochondria connected by intermitochondrial linkers and anchored to the cytoskeleton by ordered protein arrangements on the outer mitochondrial membrane4,5. This structure makes it particularly difficult to isolate sperm mitochondria. Therefore, most studies of sperm mitochondrial function use in situ analyses or demembranated sperm6.
Sperm mitochondrial structure and function have been consistently linked to male infertility7,8,9,10,11, suggesting that analysis of the structure and function of these organelles may be a good candidate for inclusion in sperm analysis.
Mitochondria play an important role in cellular energy metabolism, particularly by using oxygen to produce adenosine triphosphate (ATP) through oxidative phosphorylation (OXPHOS). In spermatozoa, in particular, the source of ATP (glycolysis vs. OXPHOS) is disputed, and much of the data remains controversial and depends on different experimental approaches4,12,13. Measurements of respiration by oximetry offer significant insights into the mitochondrial respiratory capacity, mitochondrial integrity, and energy metabolism of the cell14,15,16. Traditionally, this technique has been performed using the Clark oxygen electrode-an instrument that has been used to measure mitochondrial respiration for more than 50 years17,18. In addition, sperm mitochondrial oxygen consumption has been analyzed using the classic Clark oxygen electrode19,20,21. High-resolution respirometry (HRR) using oxygraphs (Oroboros) provides higher sensitivity than using classical respirometry devices22. The oxygraphs are composed of two chambers with injection ports, and each chamber has a polarographic oxygen sensor. With this technique, it is possible to analyze tissue slides, cells, and isolated mitochondrial suspensions. The specimen is continuously stirred in the chamber, and during the experiment, the oxygen consumption is measured, and the oxygen rates are calculated using specific software. The chambers show reduced oxygen leakage, which is an advantage over the conventional oxygen electrode devices14,23.
As with other cells, in the case of spermatozoa, the sensitivity of HRR equipment is higher than for conventional respirometry, meaning that HRR equipment can be used for the analysis of a limited number of intact or permeabilized sperm cells. There are two main strategies for assessing sperm mitochondrial function by HRR: (a) measuring the oxygen consumption in intact cells, which involves reproducing the respiratory function in a medium containing substrates such as glucose, or (b) measuring the oxygen consumption in permeabilized cells using one of the OXPHOS complexes, with the addition of specific substrates to monitor each function separately.
In the present study, we describe the use of HRR to determine mitochondrial respiration in human sperm cells.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Acid free- Bovine serum albumine</td>
			<td>Sigma Aldrich</td>
			<td>A8806</td>
			<td></td>
		</tr>
		<tr>
			<td>Adenosine 5&#39;-diphosphate monopotassium salt dihydrate</td>
			<td>Sigma Aldrich</td>
			<td>A5285</td>
			<td></td>
		</tr>
		<tr>
			<td>Animycin A from streptomyces sp.</td>
			<td>Sigma Aldrich</td>
			<td>A8674</td>
			<td></td>
		</tr>
		<tr>
			<td>Calcium chloride</td>
			<td>Sigma Aldrich</td>
			<td>C4901</td>
			<td></td>
		</tr>
		<tr>
			<td>carbonyl cyanide-P- trifluoromethoxy-phenylhydrazone</td>
			<td>Sigma Aldrich</td>
			<td>C2920</td>
			<td></td>
		</tr>
		<tr>
			<td>DatLab sofware version 4,2</td>
			<td>Oroboros Instruments GmbH</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>D-glucose</td>
			<td>Sigma Aldrich</td>
			<td>G7021</td>
			<td></td>
		</tr>
		<tr>
			<td>Digitonin</td>
			<td>Sigma Aldrich</td>
			<td>D141</td>
			<td></td>
		</tr>
		<tr>
			<td>EGTA</td>
			<td>Sigma Aldrich</td>
			<td>E4378</td>
			<td></td>
		</tr>
		<tr>
			<td>HEPES</td>
			<td>Sigma Aldrich</td>
			<td>H3375</td>
			<td></td>
		</tr>
		<tr>
			<td>L glutamic acid</td>
			<td>Sigma Aldrich</td>
			<td>G1251</td>
			<td></td>
		</tr>
		<tr>
			<td>L malic acid</td>
			<td>Sigma Aldrich</td>
			<td>M1000</td>
			<td></td>
		</tr>
		<tr>
			<td>Magnesium sulphate</td>
			<td>Sigma Aldrich</td>
			<td>M7506</td>
			<td></td>
		</tr>
		<tr>
			<td>Microliter Syringes</td>
			<td>Hamilton</td>
			<td>87900 or 80400</td>
			<td></td>
		</tr>
		<tr>
			<td>Microscope camera</td>
			<td>Basler</td>
			<td>acA780-75gc</td>
			<td></td>
		</tr>
		<tr>
			<td>Microscope Eclipse E200 with phase contrast 10X Ph+</td>
			<td>Nikon</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Monopotassium phosphate</td>
			<td>Sigma Aldrich</td>
			<td>P5655</td>
			<td></td>
		</tr>
		<tr>
			<td>MOPS</td>
			<td>Sigma Aldrich</td>
			<td>M1254</td>
			<td></td>
		</tr>
		<tr>
			<td>Oligomycin A</td>
			<td>Sigma Aldrich</td>
			<td>75351</td>
			<td></td>
		</tr>
		<tr>
			<td>Oxygraph-2 K</td>
			<td>Oroboros Instruments GmbH</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium chloride</td>
			<td>Sigma Aldrich</td>
			<td>P3911</td>
			<td></td>
		</tr>
		<tr>
			<td>Power O2k-Respirometer</td>
			<td>Oroboros Intruments</td>
			<td>10033-01</td>
			<td></td>
		</tr>
		<tr>
			<td>Rotenone</td>
			<td>Sigma Aldrich</td>
			<td>R8875</td>
			<td></td>
		</tr>
		<tr>
			<td>Saccharose</td>
			<td>Sigma Aldrich</td>
			<td>S0389</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium bicarbonate</td>
			<td>Sigma Aldrich</td>
			<td>S5761</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium lactate</td>
			<td>Sigma Aldrich</td>
			<td>L7022</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium pyruvate</td>
			<td>Sigma Aldrich</td>
			<td>P2256</td>
			<td></td>
		</tr>
		<tr>
			<td>Sperm class analyzer 6.3.0.59 Evolution-SCA Research</td>
			<td>Microptic</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Sperm Counting Chamber DRM-600</td>
			<td>Millennium Sciences CELL-VU</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Succinate disodium salt</td>
			<td>Sigma Aldrich</td>
			<td>W327700</td>
			<td></td>
		</tr>
	</tbody>
</table>

high-resolution respirometry to assess mitochondrial function in human spermatozoa

Semen quality is often studied by routine semen analysis, which is descriptive and often inconclusive. Male infertility is associated with altered sperm mitochondrial activity, so the measurement of sperm mitochondrial function is an indicator of sperm quality. High-resolution respirometry is a method of measuring the oxygen consumption of cells or tissues in a closed-chamber system. This technique can be implemented to measure respiration in human sperm and provides information about the quality and integrity of the sperm mitochondria. High-resolution respirometry allows the cells to move freely, which is an a priori advantage in the case of sperm. This technique can be applied with intact or permeabilized spermatozoa and allows for the study of intact sperm mitochondrial function and the activity of individual respiratory chain complexes. The high-resolution oxygraph instrument uses sensors to measure the oxygen concentration coupled with sensitive software to calculate the oxygen consumption. The data are used to calculate respiratory indices based on the oxygen consumption ratios. Consequently, the indices are the proportions of two oxygen consumption rates and are internally normalized to the cell number or protein mass. The respiratory indices are an indicator of sperm mitochondrial function and dysfunction.

Determination of the optimal concentration of digitonin in sperm cells 
In this protocol, we present the use of HRR to monitor real-time changes in OXPHOS in human sperm cells. Since the method can be used to analyze intact or digitonin-permeabilized sperm, we first present the standardization of digitonin concentration required to permeabilize sperm cells (Figure 3).
Digitonin is used for chemical permeabilization, which allows substrates to...

Watch this Scientific Journal Video about Advancing Male Infertility Research by Unraveling Sperm Metabolism and Mitochondrial Function at JoVE.com

Author Spotlight: Advancing Male Infertility Research by Unraveling Sperm Metabolism and Mitochondrial Function 

The analysis of sperm mitochondrial function by high-resolution respirometry permits the measurement of the oxygen consumption of freely moving spermatozoa in a closed-chamber system. The technique can be applied to measure respiration in human spermatozoa, which provides information on sperm mitochondrial characteristics and integrity.

High-Resolution Respirometry to Assess Mitochondrial Function in Human Spermatozoa

Semen quality is often studied by routine semen analysis, which is descriptive and often inconclusive. Male infertility is associated with altered sperm ...

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1.4K Views.  Unidad Académica Histología y Embriología. The analysis of sperm mitochondrial function by high-resolution respirometry permits the measurement of the oxygen consumption of freely moving spermatozoa in a closed-chamber system. The technique can be applied to measure respiration in human spermatozoa, which provides information on sperm mitochondrial characteristics and integrity.

Video: Author Spotlight: Advancing Male Infertility Research by Unraveling Sperm Metabolism and Mitochondrial Function 

Methods to Quantify Pharmacologically Induced Alterations in Motor Function in Human Incomplete SCI

Spinal cord injury (SCI) is a debilitating disorder, which produces profound deficits in volitional motor control. Following medical stabilization, recovery from SCI typically involves long term rehabilitation. While recovery of walking ability is a primary goal in many patients early after injury, those with a motor incomplete SCI, indicating partial preservation of volitional control, may have the sufficient residual descending pathways necessary to attain this goal. However, despite physical interventions, motor impairments including weakness, and the manifestation of abnormal involuntary reflex activity, called spasticity or spasms, are thought to contribute to reduced walking recovery. Doctrinaire thought suggests that remediation of this abnormal motor reflexes associated with SCI will produce functional benefits to the patient. For example, physicians and therapists will provide specific pharmacological or physical interventions directed towards reducing spasticity or spasms, although there continues to be little empirical data suggesting that these strategies improve walking ability.
In the past few decades, accumulating data has suggested that specific neuromodulatory agents, including agents which mimic or facilitate the actions of the monoamines, including serotonin (5HT) and norepinephrine (NE), can initiate or augment walking behaviors in animal models of SCI. Interestingly, many of these agents, particularly 5HTergic agonists, can markedly increase spinal excitability, which in turn also increases reflex activity in these animals. Counterintuitive to traditional theories of recovery following human SCI, the empirical evidence from basic science experiments suggest that this reflex hyper excitability and generation of locomotor behaviors are driven in parallel by neuromodulatory inputs (5HT) and may be necessary for functional recovery following SCI. 
The application of this novel concept derived from basic scientific studies to promote recovery following human SCI would appear to be seamless, although the direct translation of the findings can be extremely challenging. Specifically, in the animal models, an implanted catheter facilitates delivery of very specific 5HT agonist compounds directly onto the spinal circuitry. The translation of this technique to humans is hindered by the lack of specific surgical techniques or available pharmacological agents directed towards 5HT receptor subtypes that are safe and effective for human clinical trials. However, oral administration of commonly available 5HTergic agents, such as selective serotonin reuptake inhibitors (SSRIs), may be a viable option to increase central 5HT concentrations in order to facilitate walking recovery in humans. Systematic quantification of how these SSRIs modulate human motor behaviors following SCI, with a specific focus on strength, reflexes, and the recovery of walking ability, are missing.
This video demonstration is a progressive attempt to systematically and quantitatively assess the modulation of reflex activity, volitional strength and ambulation following the acute oral administration of an SSRI in human SCI. Agents are applied on single days to assess the immediate effects on motor function in this patient population, with long-term studies involving repeated drug administration combined with intensive physical interventions.

This video demonstrates modulation of reflex activity, volitional strength and ambulation through clinical and quantitative assessments in individuals with motor incomplete SCI as a result of acute oral administration of a serotonin reuptake inhibitor (SSRI).

Spinal cord injury (SCI) is a debilitating disorder, which produces profound deficits in volitional motor control. Following medical stabilization, ...

In Vivo Canine Muscle Function Assay

We describe a minimally-invasive and reproducible method to measure canine pelvic limb muscle strength and muscle response to repeated eccentric 
contractions. The pelvic limb of an anesthetized dog is immobilized in a stereotactic frame to align the tibia at a right angle to the femur. Adhesive wrap affixes the 
paw to a pedal mounted on the shaft of a servomotor to measure torque. Percutaneous nerve stimulation activates pelvic limb muscles of the paw to either push (extend) or 
pull (flex) against the pedal to generate isometric torque. Percutaneous tibial nerve stimulation activates tibiotarsal extensor muscles. Repeated eccentric (lengthening) 
contractions are induced in the tibiotarsal flexor muscles by percutaneous peroneal nerve stimulation. The eccentric protocol consists of an initial isometric contraction 
followed by a forced stretch imposed by the servomotor. The rotation effectively lengthens the muscle while it contracts, e.g., an eccentric contraction. During 
stimulation flexor muscles are subjected to an 800 msec isometric and 200 msec eccentric contraction. This procedure is repeated every 5 sec. To avoid fatigue, 4 min rest 
follows every 10 contractions with a total of 30 contractions performed.

In Vivo Canine Muscle Function Assay

We describe a minimally-invasive and painless method to measure canine hindlimb muscle strength and muscle response to repeated eccentric contractions.

We describe a minimally-invasive and reproducible method to measure canine pelvic limb muscle strength and muscle response to repeated eccentric 
...

Murine Spinotrapezius Model to Assess the Impact of Arteriolar Ligation on Microvascular Function and Remodeling

The murine spinotrapezius is a thin, superficial skeletal support muscle that extends from T3 to L4, and is easily accessible via dorsal skin incision. Its unique anatomy makes the spinotrapezius useful for investigation of ischemic injury and subsequent microvascular remodeling. Here, we demonstrate an arteriolar ligation model in the murine spinotrapezius muscle that was developed by our research team and previously published1-3. For certain vulnerable mouse strains, such as the Balb/c mouse, this ligation surgery reliably creates skeletal muscle ischemia and serves as a platform for investigating therapies that stimulate revascularization. Methods of assessment are also demonstrated, including the use of intravital and confocal microscopy. The spinotrapezius is well suited to such imaging studies due to its accessibility (superficial dorsal anatomy) and relative thinness (60-200 &mu;m). The spinotrapezius muscle can be mounted en face, facilitating imaging of whole-muscle microvascular networks without histological sectioning. We describe the use of intravital microscopy to acquire metrics following a functional vasodilation procedure; specifically, the increase in arterilar diameter as a result of muscle contraction. We also demonstrate the procedures for harvesting and fixing the tissues, a necessary precursor to immunostaining studies and the use of confocal microscopy.

We demonstrate a novel arterial ligation model in murine spinotrapezius muscle, including a step-by-step procedure and description of required instrumentation. We describe the surgery and relevant outcome measurements relating to vascular network remodeling and functional vasodilation using intravital and confocal microscopy.

The murine spinotrapezius is a thin, superficial skeletal support muscle that extends from T3 to L4, and is easily accessible via dorsal skin incision. ...

A Novel High-resolution In vivo Imaging Technique to Study the Dynamic Response of Intracranial Structures to Tumor Growth and Therapeutics

We have successfully integrated previously established Intracranial window (ICW) technology 1-4 with intravital 2-photon confocal microscopy to develop a novel platform that allows for direct long-term visualization of tissue structure changes intracranially. Imaging at a single cell resolution in a real-time fashion provides supplementary dynamic information beyond that provided by standard end-point histological analysis, which looks solely at 'snap-shot' cross sections of tissue.
Establishing this intravital imaging technique in fluorescent chimeric mice, we are able to image four fluorescent channels simultaneously. By incorporating fluorescently labeled cells, such as GFP+ bone marrow, it is possible to track the fate of these cells studying their long-term migration, integration and differentiation within tissue. Further integration of a secondary reporter cell, such as an mCherry glioma tumor line, allows for characterization of cell:cell interactions. Structural changes in the tissue microenvironment can be highlighted through the addition of intra-vital dyes and antibodies, for example CD31 tagged antibodies and Dextran molecules.
Moreover, we describe the combination of our ICW imaging model with a small animal micro-irradiator that provides stereotactic irradiation, creating a platform through which the dynamic tissue changes that occur following the administration of ionizing irradiation can be assessed.
Current limitations of our model include penetrance of the microscope, which is limited to a depth of up to 900 &mu;m from the sub cortical surface, limiting imaging to the dorsal axis of the brain. The presence of the skull bone makes the ICW a more challenging technical procedure, compared to the more established and utilized chamber models currently used to study mammary tissue and fat pads 5-7. In addition, the ICW provides many challenges when optimizing the imaging.

A Novel High-resolution In vivo Imaging Technique to Study the Dynamic Response of Intracranial Structures to Tumor Growth and Therapeutics

We describe a novel in vivo imaging technique that couples fluorescent chimeric mice with intracranial windows and high-resolution 2-photon microscopy. This imaging platform aids studies of dynamic changes in brain tissue and microvasculature, at a single-cell level, following pathological insults and is adaptable to assess intracranial drug delivery and distribution.

We have successfully integrated previously established Intracranial window (ICW) technology 1-4 with intravital 2-photon confocal microscopy to develop a ...

Assessing Cortical Cerebral Microinfarcts on High Resolution MR Images

Cerebral microinfarcts are frequent findings in the post-mortem human brain, and are related to cognitive decline and dementia. Due to their small sizes it is challenging to study them on clinical MRI scans. It was recently demonstrated that cortical microinfarcts can be depicted with MRI scanners using high magnetic field strengths (7T). Based on this experience, a proportion of these lesions is also visible on lower resolution 3T MRI. These findings were corroborated with ex vivo imaging of post-mortem human brain tissue, accompanied by histopathological verification of possible cortical microinfarcts.
Here an ex vivo imaging protocol is presented, for the purpose of validating MR observed cerebral microvascular pathology with histological evaluation. Furthermore, guidelines are provided for the assessment of cortical microinfarcts on both in vivo 7T and 3T MR images. These guidelines provide researchers with a tool to rate cortical microinfarcts on in vivo images of larger patient samples, to further unravel their clinical relevance in cognitive decline and dementia, and establish these lesions as a novel biomarker of cerebral small vessel disease.

A high resolution ex vivo 7T MR imaging protocol is presented, to perform MR-guided histopathological validation of microvascular pathology in post-mortem human brain tissue. Furthermore, guidelines are provided for the assessment of cortical microinfarcts on in vivo 7T as well as 3T MR images.

Cerebral microinfarcts are frequent findings in the post-mortem human brain, and are related to cognitive decline and dementia. Due to their small sizes ...

Treating SCA1 Mice with Water-Soluble Compounds to Non-Specifically Boost Mitochondrial Function

Mitochondrial dysfunction plays a significant role in the aging process and in neurodegenerative diseases including several hereditary spinocerebellar ataxias and other movement disorders marked by progressive degeneration of the cerebellum. The goal of this protocol is to assess mitochondrial dysfunction in Spinocerebellar ataxia type 1 (SCA1) and assess the efficacy of pharmacological targeting of metabolic respiration via the water-soluble compound succinic acid to slow disease progression. This approach is applicable to other cerebellar diseases and can be adapted to a host of water-soluble therapies.
Ex vivo analysis of mitochondrial respiration is used to detect and quantify disease-related changes in mitochondrial function. With genetic evidence (unpublished data) and proteomic evidence of mitochondrial dysfunction in the SCA1 mouse model, we evaluate the efficacy of treatment with the water-soluble metabolic booster succinic acid by dissolving this compound directly into the home cage drinking water. The ability of the drug to pass the blood brain barrier can be deduced using high performance liquid chromatography (HPLC). The efficacy of these compounds can then be tested using multiple behavioral paradigms including the accelerating rotarod, balance beam test and footprint analysis. Cytoarchitectural integrity of the cerebellum can be assessed using immunofluorescence assays that detect Purkinje cell nuclei and Purkinje cell dendrites and soma. These methods are robust techniques for determining mitochondrial dysfunction and the efficacy of treatment with water-soluble compounds in cerebellar neurodegenerative disease.

We present a biochemical and behavioral protocol to evaluate the efficacy of mitochondria-targeted water-soluble compounds for the treatment of Spinocerebellar ataxia type 1 (SCA1) and other cerebellar neurodegenerative diseases.

Mitochondrial dysfunction plays a significant role in the aging process and in neurodegenerative diseases including several hereditary spinocerebellar ...

Phosphorus-31 Magnetic Resonance Spectroscopy: A Tool for Measuring In Vivo Mitochondrial Oxidative Phosphorylation Capacity in Human Skeletal Muscle

Skeletal muscle mitochondrial oxidative phosphorylation (OXPHOS) capacity, which is critically important in health and disease, can be measured in vivo and noninvasively in humans via phosphorus-31 magnetic resonance spectroscopy (31PMRS). However, the approach has not been widely adopted in translational and clinical research, with variations in methodology and limited guidance from the literature. Increased optimization, standardization, and dissemination of methods for in vivo 31PMRS would facilitate the development of targeted therapies to improve OXPHOS capacity and could ultimately favorably impact cardiovascular health. 31PMRS produces a noninvasive, in vivo measure of OXPHOS capacity in human skeletal muscle, as opposed to alternative measures obtained from explanted and potentially altered mitochondria via muscle biopsy. It relies upon only modest additional instrumentation beyond what is already in place on magnetic resonance scanners available for clinical and translational research at most institutions. In this work, we outline a method to measure in vivo skeletal muscle OXPHOS. The technique is demonstrated using a 1.5 Tesla whole-body MR scanner equipped with the suitable hardware and software for 31PMRS, and we explain a simple and robust protocol for in-magnet resistive exercise to rapidly fatigue the quadriceps muscle. Reproducibility and feasibility are demonstrated in volunteers as well as subjects over a wide range of functional capacities.

Phosphorus-31 Magnetic Resonance Spectroscopy: A Tool for Measuring In Vivo Mitochondrial Oxidative Phosphorylation Capacity in Human Skeletal Muscle

This work demonstrates the feasibility of an in vivo phosphorus-31 magnetic resonance spectroscopy (31PMRS) technique to quantify mitochondrial oxidative phosphorylation (OXPHOS) capacity in human skeletal muscle.

Skeletal muscle mitochondrial oxidative phosphorylation (OXPHOS) capacity, which is critically important in health and disease, can be measured in vivo ...

Electrophysiological Assessment of Murine Atria with High-Resolution Optical Mapping

Recent genome-wide association studies targeting atrial fibrillation (AF) have indicated a strong association between the genotype and electrophysiological phenotype in the atria. That encourages us to utilize a genetically-engineered mouse model to elucidate the mechanism of AF. However, it is difficult to evaluate the electrophysiological properties in murine atria due to their small size. This protocol describes the electrophysiological evaluation of atria using an optical mapping system with a high temporal and spatial resolution in Langendorff perfused murine hearts. The optical mapping system is assembled with dual high-speed complementary metal oxide semiconductor cameras and high magnification objective lenses, to detect the fluorescence of a voltage-sensitive dye and Ca2+ indicator. To focus on the assessment of murine atria, optical mapping is performed with an area of 2 mm &#215; 2 mm or 10 mm x 10 mm, with a 100 &#215; 100 resolution (20 &#181;m/pixel or 100 &#181;m/pixel) and sampling rate of up to 10 kHz (0.1 ms) at maximum. A 1-French size quadripolar electrode pacing catheter is placed into the right atrium through the superior vena cava avoiding any mechanical damage to the atrium, and pacing stimulation is delivered through the catheter. An electrophysiological study is performed with programmed stimulation including constant pacing, burst pacing, and up to triple extrastimuli pacing. Under a spontaneous or pacing rhythm, the optical mapping recorded the action potential duration, activation map, conduction velocity, and Ca2+ transient individually in the right and left atria. In addition, the programmed stimulation also determines the inducibility of atrial tachyarrhythmias. Precise activation mapping is performed to identify the propagation of the excitation in the atrium during an induced atrial tachyarrhythmia. Optical mapping with a specialized setting enables a thorough electrophysiological evaluation of the atrium in murine pathological models.

This protocol describes the electrophysiological evaluation of murine atria utilizing an optical mapping system with a high temporal and spatial resolution, including dual recordings of the membrane voltage and Ca2+ transient under programmed stimulation through a specialized electrode catheter.

Recent genome-wide association studies targeting atrial fibrillation (AF) have indicated a strong association between the genotype and ...

Combining Volumetric Capnography And Barometric Plethysmography To Measure The Lung Structure-function Relationship

Tools to measure lung and airways volume are critical for pulmonary researchers interested in evaluating the impact of disease or novel therapies on the lung. Barometric plethysmography is a classic technique to evaluate the lung volume with a long history of clinical use. Volumetric capnography utilizes the profile of exhaled carbon dioxide to determine the volume of the conducting airways, or dead space, and provides an index of airways homogeneity. These techniques may be used independently, or in combination to evaluate the dependence of airways volume and homogeneity on lung volume. This paper provides detailed technical instructions to replicate these techniques and our representative data demonstrates that the airways volume and homogeneity are highly correlated to lung volume. We also provide a macro for the analysis of capnographic data, which can be modified or adapted to fit different experimental designs. The advantage of these measures is that their advantages and limitations are supported by decades of experimental data, and they can be made repeatedly in the same subject without expensive imaging equipment or technically advanced analysis algorithms. These methods may be particularly useful for investigators interested in perturbations that change both the functional residual capacity of the lung and airways volume.

Here, we describe two measures of pulmonary function &#8211; barometric plethysmography, which allows the measurement of lung volume, and volumetric capnography, a tool to measure the anatomic dead space and airways uniformity. These techniques may be used independently or combined to assess airways function at different lung volumes.

Tools to measure lung and airways volume are critical for pulmonary researchers interested in evaluating the impact of disease or novel therapies on the ...

Precision Implementation of Minimal Erythema Dose (MED) Testing to Assess Individual Variation in Human Inflammatory Response

Minimal erythema dose (MED) testing is frequently used in clinical settings for determining the smallest amount of ultraviolet (UV) irradiation necessary to produce erythema (inflammatory reddening) on the surface of the skin. In this context, the MED is regarded as a key factor in determining starting doses for UV phototherapy for common skin conditions such as psoriasis and eczema. In research settings, MED testing also has potential to be a powerful tool for assessing within- and between-persons variation in inflammatory responses. However, MED testing has not been widely adopted for use in research settings, likely owing to a lack of published guidelines, which is a barrier to obtaining reproducible results from this assay. Also, protocols and equipment for establishing MED vary widely, making it difficult to compare results across laboratories. Here, we describe a precise and reproducible method to induce and measure superficial erythema using newly designed protocols and methods that can easily be adapted to other equipment and laboratory environments. The method described here includes detail on procedures that will allow extrapolation of a standardized dosage schedule to other equipment so that this protocol can be adapted to any UV radiation source.

Precision Implementation of Minimal Erythema Dose MED Testing to Assess Individual Variation in Human Inflammatory Response

Minimal erythema dose (MED) testing is used to establish dosage schedules for ultraviolet radiation phototherapy. It can assess individual variation in inflammatory response but lacks methodology for achieving reproducible results. Here, we present a precision implementation of MED and demonstrate its ability to capture individual variation in inflammatory response.

Minimal erythema dose (MED) testing is frequently used in clinical settings for determining the smallest amount of ultraviolet (UV) irradiation necessary ...